Although noise generated by pneumatic tires has various causes, among these, cavity resonance near 200 to 250 Hz generated by vibration of the air filling the tires and road noise in the middle frequency range (315 Hz band in ⅓ octave band) generated by a transfer of tire vibration caused by uneven road surfaces are transmitted into a vehicle cabin, causing passengers discomfort.
Of these, the cavity resonance in the low frequency range is air column resonance caused when air vibrations travel through the cavity of circular tires, which form air columns As ways to reduce this cavity resonance, many methods have been suggested wherein noise is absorbed by a noise-absorbing member including a porous material such as urethane foam or the like provided within the cavity between the tire and the rim of the wheel.
However, as the technical concept behind these suggested technologies involves the absorption of noise generated in the tire cavity by means of the noise-absorbing members, effects cannot be achieved unless the provided noise-absorbing members are of at least a certain volume. This can cause problems during the rim-mounting process as the noise-absorbing members occupy a considerable amount of space within the tires. Also, there is a problem of a deterioration of the noise-absorbing members over long-term use leading to reduced noise absorption performance, thus failing to achieve the desired noise prevention effect.
Furthermore, as the noise-absorbing members formed from porous material are intended exclusively to reduce cavity resonance, which is caused by the vibration of air, it has almost no effect on the reduction of road noise in the middle frequency range caused by the vibration of the tire. Accordingly, such members do not produce the effect of reducing noise generated inside cars in bands other than that of cavity resonance.